1. Field
Embodiments of the present invention generally relate to magnetic data recording, and more particularly to a structure for preventing pole erasure and thermally induced pole tip deformation in a write head.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider towards the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Most recently researchers have focused on the development of perpendicular magnetic recording (PMR) systems in order to increase the data density of a recording system. Such perpendicular recording systems record magnetic bits of data in a direction that is perpendicular to the surface of the magnetic medium. A write head used in such a system generally includes a write pole having a relatively small cross section at the ABS and a return pole having a larger cross section at the ABS. A magnetic write coil induces a magnetic flux to be emitted from the write pole in a direction generally perpendicular to the plane of the magnetic medium. This flux returns to the write head at the return pole where the flux is sufficiently spread out and weak that the flux does not erase the signal written by the write pole.
In order to meet ever increasing demand for improved data rate and data capacity, researchers are constantly seeking ways to make read and write heads smaller while increasing the write field produced by such write heads. Increasing the overwrite field requires increasing the current flow through the write coil. Decreasing the size of the write head requires decreasing the size of the write coil (decreasing the cross sectional area of the turns of the coil), which increases the electrical resistance of the coil.
This decrease in size and increase in write current greatly increases the amount of heat generated by the write head during use. This heat causes unwanted thermal expansion of the write head, which can result in catastrophic deformation of the write head structure. This deformation is especially problematic in current and future magnetic heads, where the fly height of the head is exceedingly small, on the order of nanometers. The thermal protrusion of the write head, combined with these low fly heights can result in catastrophic head disk contact during use. To reduce the thermal protrusion of the write head, a stiff plate with low coefficient of thermal expansion (CTE) has been used to provide constraint for thermal pole tip protrusion (PTR). However, such method fundamentally utilizes stress transfer from the stiff insert to the rest of the head. As such, the generation of stresses may also affect the main pole magnetic properties due to relative large positive magnetostriction effect of CoFe alloys currently being used. The stresses generated may favor a magnetization state such that its orientation may align unfavorably causing high remanence and unintended pole erasure by the write head. Therefore, an improved magnetic device having a reduced tendency for write pole erasure is needed when managing PTR through stress transfer.